Bunyaviridae are important pathogens in vertebrates and humans with over 350 members spread over many parts of the world. Many of them cause severe health problems and some are now classified as potential biological weapons in bioterrorism. Currently there are no available vaccines or treatments. Human activity and climate change are known factors favoring the emergence, reemergence, and rapid spread of virus diseases, including Bunyaviridae such as Hantavirus, a recent example that these viruses must be taken seriously as potential emerging agents of disease. Relatively little is known about Bunyaviridae. Their strategies for transmission and infection are poorly understood. The pathways and cellular factors involved in cell attachment and uptake of viral particles remain largely undefined. Part of the reason has been the large number of different virus targets and the high pathogenicity of many of the isolates. The main objective of this proposal is to identify and characterize the cellular factors involved in the attachment of Bunyaviridae at the cell surface and in the subsequent pathways taken by these viruses to enter cells and reach the cytoplasm. To achieve this goal, we will use various cell biology and molecular approaches, including light and electron microscopic methods and FACS techniques, combined with a large panel of perturbants of cellular entry pathways. To obtain a detailed list of the cellular factors involved, we will use an automated high-throughput siRNA silencing screen which has already been successfully used by our laboratory and our collaborators for many other viruses. We expect to obtain a detailed view of the cellular mechanisms involved in the Bunyaviridae entry, and contribute to a better understanding of the general cellular endocytosis machinery. The factors identified may also serve as potential targets to develop cellular-based anti-Bunyaviridae agents that block infection.